§ 1.1 Field of the Invention
The present invention generally concerns atmospheric pressure plasma generation devices (or “plasma sources”). In addition, the present invention also concerns applications for this microwave plasma torch as well as the feasibility of enlarging the device for generating multiple torches simultaneously.
§ 1.2 Background
Atmospheric pressure plasma sources may be used in applications requiring plasmas to be exposed directly to the open air. The applications include spray coating and materials synthesis (See, e.g., the articles: M. I. Boulos et al., “Thermal Plasma Fundamentals and Applications,” Vol. 1, Plenum Press, 1994, pp. 33–47 and 403–418 (hereafter referred to as “the Boulos article”); and “Thermal Plasma Torches and Technologies,” Vol. 1, O. P. Solonenko, Ed., Cambridge: Cambridge Int. Sci. Publ., 2001 (hereafter referred to as “the Solonenko article”).), microwave reflector/absorber (See, e.g., the articles: R. J. Vidmar, “On the use of atmospheric pressure plasmas as electromagnetic reflectors and absorbers,” IEEE Trans. Plasma Sci., Vol. 18, pp. 733–741, 1990 (hereafter referred to as “the Vidmar article”); and E. Koretzky and S. P. Kuo, “Characterization of an atmospheric pressure plasma generated by a plasma torch array,” Phys. Plasmas, Vol. 5, pp. 3774–3780, 1998 (hereafter referred to as “the Koretzky article”).), shock wave mitigation for sonic boom and wave drag reductions in supersonic flights (See, e.g., the articles: V. P. Gordeev et al., “Plasma technology for reduction of flying vehicle drag,” Fluid Dynamics, Vol. 31, pp. 313–317, 1996 (hereafter referred to as “the Gordeev article”); S. P. Kuo et al., “Observation of shock wave elimination by a plasma in a Mach-2.5 flow,” Phys. Plasmas, Vol. 7, pp. 1345–1348, 2000 (hereafter referred to as “the Kuo article”); and Daniel Bivolaru and S. P. Kuo, “Observation of supersonic wave mitigation by plasma aero-spike,” Phys. Plasmas, vol. 9, 721–723, 2002 (hereafter referred to as “the Bivolaru article”).), and sterilization and chemical neutralization (See, e.g., the articles: M. Laroussi, “Sterilization of contaminated matter with an atmosphere pressure plasma,” IEEE Trans. Plasma Sci., Vol. 24, pp. 1188–1191, 1996 (hereafter referred to as “the Laroussi article”); J. R. Roth et al., “A remote exposure reactor (RER) for plasma processing and sterilization by plasma active species at one atmosphere,” IEEE Trans. Plasma Sci., Vol. 28, pp. 56–63, 2000 (hereafter referred to as “the Roth article”); and H. W. Herrmann et al., “Decontamination of chemical and biological warfare (CBW) agents using an atmospheric pressure plasma jet (APPJ),” Phys. Plasma, Vol. 6, pp. 2284–2289, 1999 (hereafter referred to as “the Herrmann article”).).
Different applications have different requirements on the plasma parameters, such as its density, temperature, volume and flow rate. For spray coating application, a plasma jet is used for heating and acceleration of particles injected into the jet. Thus a high enthalpy jet having large plasma flow rate and density is desirable. Dense, uniform, low temperature, and large volume plasma is desirable for microwave reflector/absorber applications. Used for decontamination of chemical and biological warfare (CBW) agents, a plasma source is aimed at producing chemically active species, such as molecular oxygen in metastable states and atomic oxygen. These reactive species are capable of rapidly destroying a broad spectrum of CBW agents. Some of the applications also favor that the sources can be easily transported.
Dense atmospheric-pressure plasma can be produced through dc/low frequency capacitive or high frequency inductive arc discharges. This technique requires adding gas flows to stabilize the discharges and to carry the generated plasmas out of the discharge regions to form torches. The inductive torch (See, e.g., the article: T. B. Reed, “Induction-coupled plasma torch”, J. Appl. Phys., Vol. 32, pp. 821–824, 1961 (hereafter referred to as “the Reed article”).) and non-transferred dc torch (See, e.g., “the Boulos article” and M. Zhukov, “Linear direct current plasma torches”, Thermal Plasma and New Material Technology, Vol. 1: Investigations of Thermal Plasma Generators, O. Solonenko and M. Zhukov, Ed. Cambridge Interscience Publishing, pp. 9–43, 1994, (hereafter referred to as “the Zhukov article”).) employ high current power supply and require very high gas flow rate to achieve stable operation. Consequently, the structures of these torches are relatively large and are therefore unsuitable for certain applications.
Torch modules such as those described in the article S. P. Kuo, et al., “Design and electrical characteristics of a modular plasma torch,” IEEE Trans. Plasma Sci., vol. 27, no. 3, pp. 752–758, 1999; and U.S. Pat. No. 6,329,628 titled “Methods and Apparatus for Generating a Plasma Torch,” (“the '628 patent”) can be run in dc or low frequency ac mode and can produce low power (hundreds of watts) or high power (a few kW in 60-Hz periodic mode or hundreds of kW in pulsed mode) torch plasmas. However, the size of the torch plasma produced by such modules may be limited by the gap between the electrodes and may depend strongly on the gas flow rate.
In view of the foregoing deficiencies of known plasma torches, there is a need for a plasma source that is portable and that can generate a stable and sizable plasma torch independent of the gas flow rate.